1. Field of the Invention
This invention relates to the use of optical techniques to permit the analysis of a biological or medical sample for the presence of multiple types of target molecules.
2. Discussion of Related Art
Biological assays that rely on pairs of bioreceptor-target molecules are well known, such as antibody-antigen reactions. Typically, one of the molecules is immobilized on a surface and a fluid sample containing the analyte is either applied to that surface or flowed over it through a suitable flow channel. The binding of the target to the bioreceptor, generally, produces an observable physical effect, such as a change in optical properties near the surface. Many of the most widely used assays rely on fluorescence changes when the target binds to the bioreceptor. This requires special molecular structure which, if not already present in the bioreceptor or the target, must be added by chemical means. Such addition is generally referred to as fluorescent labeling or ‘tagging.’
It is generally desirable to be able to make simultaneous assays for multiple targets in a single sample. One common method of doing this is to create spatial arrays of bioreceptor regions in which each region of the array contains a different bioreceptor, each sensitive to a different target. Once the sample has interacted with the surface, imaging of the surface, for example, using fluorescence, then identifies which bioreceptor sites have changed their fluorescence, indicative of binding of the target. When using fluorescence, it is necessary to select the excitation wavelength so that fluorescence is excited and also to detect the emitted light at its appropriate wavelength.